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RE: OMEGA BLOCK with mixture model?

From: Mark Sale - Next Level Solutions <mark>
Date: Tue, 14 Apr 2009 08:46:23 -0700

 You'll need to rearrange/reassign your ET= As so that you can have correlation between CL(1) and F1, and CL(2) and F1,= but not CL(1) and CL(2).  So, put ETA(1) on CL(1), ETA(2) on F1 and E= TA(3) on CL(2), then $OMEGA like this:

0.1=             &n= bsp;       ;CL(1)
0.01 0.1       &nbs= p;     ;F1
0 =      0.01   0.1  ;CL(2)

This is= the BAND matrix, which is permitted.

Mark Sale MD
Next Level Solutions, LLC

-------- Original Message --------
Subject: [NMusers] OMEGA BLOCK with mixture model?
From: nele.plock Date: Tue, April 14, 2009 11:08 am
To: nmusers

Dear all,

I am trying to fit a PK model to oral data. I= n the data, we observed two things: First, CL seems to be negatively correl= ated with F1. Secondly, there seem to be two subpopulations in the exposure= , let's say a large group with 'normal' and a second group with high exposu= re. I would like to identify the subpopulations using a mixture model, but = keep the correlation between CL and F1. Now I ran into problems when coding= the $OMEGA BLOCK.

I f= igured the block to be something like:
0.1  ;CL1
0 FIX 0.1 ;= CL2
0.01 0.01 0.1 ;F1

The error message that appe= ars is:
a covariance is zer= o, but the block is not a band matrix

I assume that this means that I am not allowed to fix the c= orrelation between the two clearance-omegas to zero. However, it would be u= nreasonable to allow a correlation, because the omegas belong to different = subpopulations, so there can't be a correlation. On the other hand, I did n= ot include subpopulations for F1, so how can I keep this correlation to bot= h CL-subgroups?

Any th= oughts on this would be highly appreciated!
Best wishes
____________________= __________________________________________

Dr. Nele Plock
Phar= macometrics -- Modeling and Simulation

Nycomed GmbH
Byk-Gulden= -Str. 2
D-78467 Konstanz, Germany

Fon: (+49) 7531 / 84 -  = ;4759
Fax: (+49) 7531 / 84 - 94759

mailto: nele.plock com

County Court: Fre= iburg, Commercial Register HRB 701257
Chairman Supervisory Board: Charl= es Depasse
Management Board: Dr. Barthold Piening, Gilbert Rademacher, = Dr. Anders Ullman

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Received on Tue Apr 14 2009 - 11:46:23 EDT

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